Mainly un-satisfied quality silicon for semiconductor use has been previously utilized as the silicon for the solar cells, in that case, problems for the supply of enough amount are remained to satisfy the big increasing of demand for solar cells. From these, so-called metal melting process, where the reaction between molten zinc and silicon tetra-chloride is performed, is known for the independent supply of silicon, but has the problems of products having powdery and complicated treatment, difficulty of impurity treatments and also the difficulty of casting, which will result high cost, so the process has not been utilized.
To dissolve the problems, silicon production process by gas phase zinc reducing process was proposed, but together with the silicon produce, about ten times of amount of zinc chloride (ZnCl2) is co-produced and the disposal of it must be troublesome, so the commercial application of this process is very limited. Recently, as described in JP-A-11(1999)-92130, silicon production process by spraying silicon tetra-chloride to molten zinc and then formed zinc-chloride is electrolyzed to taking out zinc and chlorine, where formed chlorine is taking out as hydrochloric acid and used for production of silicon tetra-chloride, has been proposed. From the point of view of reuse of zinc chloride, the objective has been established, but actually produced silicon is mixture of molten zinc and silicon itself became fine powders, so formed silicon particle having big surface area, then purification became difficult, which was big problem.
Also processes using mono-silane, di-silane, or tri-chloro silan as raw material is known, in which the reaction rate is low and then both the energy consumption for producing silicon becomes big and recovery of co-existed hydrogen becomes big problems. Not limiting to hydrogen, disposing of co-produced chlorine and hydrochloric acid must be big problem also in this process, it is said to be difficult to reduce the cost, because hydrogen, which is rather expensive, must be used as the reducing materials.
Otherwise, to obtain single crystal silicon from poly-crystalline or powdered silicon obtained under these processes, it must have less problem when those silicon poly-crystalline materials having rather big particle size and relatively small surface area are used, because those materials have less absorption of impurities and oxygen, but in the case of silicon being fine powder and having high surface area, removal of surface absorbed materials is required before installing to the crystal growing processes though such silicone bulk is very pure because the absorbed materials must be caused of impurity, which gives complicated procedure and requires treatment of abolishes. Then the producing cost must become high. And according to the normal process, complicated processes of high temperature treatment being applied at first to produce silicon powder or fine crystalline, then cooling and then heating to melt are required, and which requires repeating heating/cooling, which gives also troublesome from the energy consumption.
Especially in these processes, each process is independent, so the workability is not bad but the process requiring big heat input/output is permissible for the manufacture of high value added ones of electronics devices, but for the use as solar cells, which must be the main usage, in which very low price and less energy consumption must be the main target, though very big amount of demand is expected. No technologies to satisfy these targets have been known.
As shown in the above, previous technologies are all mainly aimed silicon to grown as solid or crystalline, so the formed crystal blocks or powder is considered to be exposed in air where once formed silicon is re-refined according to the requirement, then re-melt or crystallization is performed, when in grown single crystals or grown poly-crystalline, where at least excess energy is required for re-melting. And when in producing silicon blocks or powders, as the materials, is premised to expose in air, block silicon is preferred to minimize the impurity absorption when in producing silicon raw material, then reducing process of silicon tetra-chloride by zinc, which is the simplest way of producing silicon, could not be applied in the commercial process, which has also big problem. Recently, some trials of direct taking out of molten silicon from the reaction furnace is performed, but several problems such as corrosion by co-product hydrochloric acid and reaction between furnace wall and silicon, which gives shortening of furnace life, due to high operation temperature, have been arisen.
And application of smaller reacting furnace and higher efficiency of reaction are desirable when in applying to the production of high purity silicon by gas phase reaction of silicon tetra-chloride and zinc of previous technology.